1. Field
Certain embodiments of the invention generally relate to timing and synchronization in communications networks, such as packet switched networks.
2. Description of the Related Art
The Precision Time Protocol (PTP), as originally defined in the institute of Electrical and Electronics Engineers (IEEE) 1588 standard, is a protocol used to synchronize clocks throughout a computer or communications network. On a local area network, for example, PTP may achieve clock accuracy in the sub-microsecond range. IEEE 1588 version 2 defines a PTP with improved accuracy but that is not backwards compatible with the original version.
The IEEE 1588 standards describe a hierarchical master-slave architecture for clock distribution. In particular, IEEE 1588 describes a time distribution system that includes at least one communication media and clocks. An ordinary clock is included in a device with a single network connection and is either the source of or destination for a synchronization reference. The source device may be referred to as a master node; the destination device may be referred to as a slave node. A boundary clock is included in a device with multiple network connections and can accurately bridge synchronization from one network segment to another. A synchronization master is selected for each of the network segments in the system.
IEEE 1588v2 introduces a clock associated with network equipment used to convey PTP messages. This transparent clock modifies PTP messages as they pass through the device. Timestamps in the messages are corrected for time spent traversing the network equipment thereby improving distribution accuracy by compensating for delivery variability across the network.